Field of the Invention
The present invention relates to a liquid crystal display (LCD) device. More particularly, the present invention relates to a method for reducing a ripple caused by the common voltage.
Discussion of the Related Art
Flat panel display (FPD) devices are applied to various electronic devices such as portable phones, tablet personal computers (PCs), notebook computers, etc. The FPD devices include liquid crystal display (LCD) devices, plasma display panels (PDPs), organic light emitting diode (OLED) display devices, etc. Recently, electrophoretic display (EPD) devices are widely used as the FPD devices.
In the FPD devices, especially, the LCD devices can be applied to all electronic devices ranging from small devices to large devices, and thus are being widely used.
Liquid crystal injected into an LCD device is driven according to a voltage difference between a data voltage supplied to a pixel electrode and a common voltage supplied to a common electrode to change a light transmittance, thereby enabling an image to be displayed.
FIG. 1 is an exemplary diagram illustrating a configuration of a related art LCD device.
The related art LCD device, as illustrated in FIG. 1, includes a panel 10 in which a plurality of pixels are respectively formed in a plurality of areas defined by a plurality of gate lines and a plurality of data lines and liquid crystal is charged into the pixels, at least one or more source driving ICs 30 that output data voltages to the respective data lines, at least one or more gate driving ICs 20 that sequentially output a scan signal to the gate lines, a timing controller 40 that controls the source driving ICs 30 and the gate driving ICs 20, and a power supply 50 that supplies a common voltage to a common electrode 12 formed in the panel 10.
The LCD device having the above-described configuration is generally driven by an inversion system in which a polarity of a data voltage applied to each liquid crystal cell is periodically inverted, for preventing the liquid crystal charged into the panel 10 from being deteriorated.
When the LCD device is driven by the inversion system, an image quality of the LCD device can be degraded depending on a correlation between a polarity of a data voltage charged into each pixel and a pattern of input image data.
The reason is because, due to data voltages charged into the respective pixels, polarities of the data voltages charged into the respective pixels may not have a balance between the positive polarity and the negative polarity in number, and one of the positive polarity and the negative polarity becomes the dominant polarity, causing a shift of the common voltage applied to the common electrode.
When the common voltage is shifted, a reference electric potential of each pixel is shaken, and for this reason, a user can feel a crosstalk, a flicker, a ripple, or a smear from an image displayed by the LCD device.
The related art LCD device uses the following methods for preventing a noise such as a ripple caused by the shift of the common voltage.
First, in terms of a structure of the related art LCD device, the common electrode is formed to minimize a resistance of the common electrode, and a circuit is configured to reduce a parasitic capacitance.
Second, in terms of a method of the related art LCD device, as illustrated in FIG. 1, a common voltage feedback compensation circuit 60 using an inverting operational amplifier is used.
However, due to a physical limitation, a solution to the device structure has a limitation in solving the above-described defects.
Moreover, in a solution to the driving method, because a Resistance/capacitance (R/C) differential occurs depending on a position of the common electrode 12, it is not easy to compensate for the common voltage all over the entire area of the panel 10, and when an input resistance of a common voltage line through which the common voltage is transferred is large, a compensation effect is weak. Especially, an R/C differential occurs between an upper end and lower end of the panel 10, and thus, when the compensation circuit 60 is optimized for compensating for a ripple caused by the common voltage, the common voltage applied to the upper end is overcompensated, causing a C/T defect to be intensified.
That is, as the demand for a narrow bezel increases, a width of the common voltage line decreases in designing the panel 10, and thus a resistance of the common voltage line increases, causing an increase in load of the common voltage line. For this reason, the related art compensation circuit 60 using a common voltage feedback (Vcom FB) is reduced in efficiency, causing problems such as C/T.